Titan was a major focus of the mission all along, since it's bigger than the planet Mercury and the only moon massive enough to have a significant atmosphere.
土卫六一直以来都是这项探测任务的主要聚焦点，因其体积比水星还要大，是唯一一颗拥有浓密大气层的卫星。
Finally, planetary scientists are eager to learn where Titan's nitrogen and methane originated and why it is the only moon in the solar system that possesses a dense atmosphere.
最后，行星科学家急于了解土卫六的氮气及甲烷从何而来，又为什么只有它是太阳系唯一拥有浓密大气的卫星。
It is the only moon of any planet which has its own atmosphere.
TITAN是所有行星的卫星中唯一有自己的大气层的卫星。
It is the only moon of any planet which has its own atmosphere.
TITAN是所有行星的卫星中唯一有自己的大气层的卫星。
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